Aspiration has been used as a method to remove thrombotic blockages from blood vessels. For example, a single lumen catheter is sometimes used to aspirate a clot from a cerebral vessel in an acute ischemic stroke patient. Such a procedure generally entails placing a distal tip of a catheter at the proximal face of the clot and applying vacuum to the clot via a proximal port of the catheter. The clot may be soft enough to be aspirated into the catheter, or in cases of harder clots aspiration on the catheter attaches the clot to the distal tip of the catheter and the attached clot removed together with the catheter. In some cases, the clot is broken up by mechanical means during aspiration, to aid in aspiration of the clot through the catheter.
The aspiration source may be a suction pump or simply a syringe, each of which has pros and cons. An advantage of a syringe is that a syringe can generate near full vacuum by the user pulling back forcefully on the syringe plunger to generate a strong force. This force is somewhat independent of the size of the syringe, in that even a small syringe can generate near full vacuum. A larger syringe size simply allows a greater amount of fluid and/or clot to be aspirated during one “pull back”.
The syringe also allows the user to “feel” if the distal end of the catheter is blocked by the tactile feedback of a counter force on the plunger of the syringe. The syringe also allows the user to easily vary the force and/or rate of suction. However, there are also some disadvantages of a syringe. A syringe is designed for controlled one-handed injection into the vessel, which is not optimally designed for one-handed pull back or aspiration from the vessel. To maintain a full vacuum requires constant manual hold on the syringe barrel and plunger, which can be cumbersome. If the user wishes to let go of the syringe momentarily, the vacuum may be lost. A locking syringe may be used to counter this by permitting the user to lock the syringe in a vacuum state. But such locking syringes require two hands to lock, and usually only lock in discrete positions. Moreover, locking the syringe in full pull-back would remove the “feel” of the syringe plunger. In addition, once a syringe is filled, it needs to be removed, emptied, and reattached to the catheter if further aspiration is desired. These extra steps require a pause in the procedure, a loss of vacuum when the syringe is detached unless a stopcock is used, and two hands to remove the syringe.
In contrast, the suction pump is advantageous in that it is “hands free” and has unlimited length of time for suction without the need to pause, as compared to a syringe. However, there are limitations to the suction pump. First, there is limited aspiration force as compared to a syringe, due to the dead air space in the pump. Second, the user does not have the “feel” of suction and therefore may not realize if and when the distal tip of the catheter is clogged. In cases where the catheter does not aspirate the clot but acts as a suction attachment whereby the clot can be pulled back, knowing when the catheter “loses” vacuum can be critical. Some users will gently move the catheter forward to re-engage the clot with the suction at the tip of the catheter when they feel this loss. This feature is not so important when the pump is used with systems that break up a clot, as in this case all the clot is aspirated through the lumen of the catheter. However, there is clinical benefit to being able to remove the clot in one piece, or in as large a section as possible due to the fact that there is less potential for pieces of clot to break off and flow distally into the brain.
A disadvantage of all current aspiration devices is the standard connection to the catheter. Standard catheters have a female Luer connector on the proximal end of the catheter. Any device connecting to the female Luer connector has a male Luer connector. This type of connection creates a flow restriction and a step inside the Luer connection, which may cause a clot or a portion of a clot to catch on the step, especially in cases where a large volume clot is being aspirated in one piece. Not only does this interfere with aspiration, but there is risk that the clot caught in the connector would be flushed back into the brain when the user flushes contrast or other solution through the catheter.